I have a laptop with Intel i3 370M (SSE 4.1), 4GB RAM, Radeon HD 5650 1GB.
When playing Tekken 5, the number of fps is low (20 - 30 fps) which is curious because a lot better computer games works without a problem.
I have 0.9.8 version and the latest DirectX.
What should be the optimal configuration? I tried to change the configuration, but it did not improve the number of fps.

Im not sure enought about how well playing Tekken 5 on pcsx2 0.98 but i already tested this game in the past and this game was working well for me almost with full speed all the time with old pcsx2 0.96 beta which still has vu skip hack in option mix with vu cycle stealing option i messed with both. Perhaps you can try with those at least.
Edit :
Make sure you have to set native option in gsdx plugin because this game is one of demanding games for eating GPU but fortunely this game has progressif scan option in game menu for better visual quality.